IDivision of Diabetes Translation, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America. Send correspondence to Xuanping Zhang, xbz2@cdc.govIIU.S.- Mexico Border Office, Pan American Health Organization, El Paso, Texas, United States of America IIISchool of Medicine, Louisiana State University, New Orleans, Louisiana, United States of America

ABSTRACT

OBJETIVE: To examine the relationship between access to health care and undiagnosed diabetes among the high-risk, vulnerable population in the border region between the United States of America and Mexico. METHODS: Using survey and fasting plasma glucose data from Phase I of the U.S.-Mexico Border Diabetes Prevention and Control Project (February 2001 to October 2002), this epidemiological study identified 178 adults 1864 years old with undiagnosed diabetes, 326 with diagnosed diabetes, and 2 966 without diabetes. Access to health care among that sample (n = 3 470), was assessed by type of health insurance coverage (including "none"), number of health care visits over the past year, routine pattern of health care utilization, and country of residence. RESULTS: People with diabetes who had no insurance and no place to go for routine health care were more likely to be undiagnosed than those with insurance and a place for routine health care (odds ratio [OR] 2.6, 95% confidence interval [CI] 1.06.6, and OR 4.5, 95% CI 1.414.1, respectively). When stratified by country, the survey data showed that on the U.S. side of the border there were more people with undiagnosed diabetes if they were 1) uninsured versus the insured (28.9%, 95% CI 11.5%46.3%, versus 9.1%, 95% CI 1.5%16.7%, respectively) and if they 2) had made no visits or 13 visits to a health care facility in the past year versus had made > 4 visits (40.8%, 95% CI 19.6%62.0%, and 23.4%, 95% CI 9.9%36.9%, respectively, versus 2.4%, 95% CI 0.9%5.7%) (all, P < 0.05). No similar pattern was found in Mexico. CONCLUSIONS: Limited access to health careespecially not having health insurance and/or not having a place to receive routine health serviceswas significantly associated with undiagnosed diabetes in the U.S.-Mexico border region.

The United States of America and Mexico share a border that links four U.S. and six Mexican states.1 The border region, which extends 100 km north and south of the political divide and 3 141 km from the Gulf of Mexico to the Pacific Ocean, links two nations with considerable differences in terms of types of health care systems and level of economic development (1). On both sides of the border, undiagnosed diabetes is associated with tremendous human and economic costs.

In the United States, an estimated 5.7 million people with diabetes24% of the 23.6 million people suffering from diabetes nationwidewere undiagnosed, according to a 2007 study (2). In Mexico, a survey published in 2002 targeting the urban population aged 20 to 69 years indicated 26% of people with diabetes aged 40 years or older and 42% of those aged 2040 years old were unaware of their condition (3). Complications of diabetes include blindness, kidney failure, cardiovascular disease, and conditions that require lower-limb amputations (4). There are many efficacious and costeffective interventions that can prevent or delay these complications, but none would be carried out among people with diabetes who are unaware of their condition (4). Therefore, timely detection of diabetes is crucial (57).

In the United States, according to U.S. Census Bureau estimates for 2008, 15.4% or 46 million people lacked health insurance (8). By 2009, the estimated number had grown to 52 million (9). In Mexico, data for 2001 from a nationally representative prospective panel study known as the Mexican Health and Aging Study (Estudio Nacional de Salud y Envejecimiento en México) indicated 39% of Mexican adults aged 50 years or older were uninsured (10). Although several initiatives have been launched in Mexico to expand health insurance coverage, as well as access to health care, including the conditional cash transfer Oportunidades program targeting poor families with children (formerly known as Progresa), and the Seguro Popular de Salud program targeting the uninsured, they have not resulted in substantial improvements (11). While data for the U.S.-Mexico border region in particular is relatively limited, studies that have been conducted indicate similar gaps in health insurance coverage. In the four U.S. states that border Mexico, the percentage of uninsured was 21% in the counties that border Mexico and 14% in the counties that do not (12).

Studies in both the United States and Mexico indicate that, compared to those with insurance, the uninsured are much less likely to receive routine checkups or preventive services (13, 14), tend to be more severely ill when diagnosed, and receive less therapeutic care (15). Not only does insurance coverage play a role in access to preventive care (16), but absence of a place to go for routine health care, which is related to lack of health insurance, is also associated with the absence of screening, follow-up care, and pharmacologic treatment for hypertension (17). Limited access to health care not only affects the use of preventive services (18) but also elevates the risk of a decline in overall health (19) and is associated with undiagnosed diabetes along with other health conditions (20).

Limited access to health care is one of the challenges faced by people living in the U.S.-Mexico border region. This study examined how various health care access indicators, including insurance coverage, affects the detection of diabetes among the high-risk, vulnerable population in the U.S.-Mexico border region, and whether the relationship differs between the two countries.

MATERIALS AND METHODS

Data

This epidemiological study used survey and fasting plasma glucose data from Phase I (February 2001 to October 2002) of the U.S.-Mexico Border Diabetes Prevention and Control Project (21). Phase I was a population-based, cross-sectional study of a multistage cluster representative sample of 4 027 adults aged 18 years or older living in the 10 contiguous states of the U.S.-Mexico border region.

The project survey included a questionnaire with 65 questions about diabetes, general health and access to health care, hypertension, physical activity, diet and eating habits, tobacco use, alcohol consumption, reproductive health, socio-cultural aspects, acculturation, education, work history, and demographic characteristics, including ethnicity (21). Bilingual interviewers administered the questionnaire in either English or Spanish, depending on the preference of each individual respondent. Weight and height were measured and used to calculate body mass index (BMI). As per World Health Organization (WHO) standards, BMI categories were defined as follows: underweight < 18.5, normal weight 18.524.9, overweight 2529.9, and obesity > 30.0. Systolic and diastolic blood pressure levels were measured in triplicate. Venipuncture was performed after 8-hour fasting to obtain fasting plasma glucose (21).

The current study's analyses were based on project survey data for adults aged 18 to 64 years who had fasted for 8 hours or longer immediately before having their plasma glucose measured (n = 3 470). Persons aged 65 years or older were excluded to screen out recipients of Medicare (a U.S. federal government health care insurance program available to those in that age group). Survey respondents were classified as having diagnosed diabetes if they responded positively to the question "Have you ever been told by a doctor or other health care worker that you have diabetes or high blood sugar?" Women who had diabetes only during pregnancy were excluded. Survey respondents who had not been told that they had diabetes but had a fasting plasma glucose level > 126 mg/dL were classified as having undiagnosed diabetes while those with fasting plasma glucose levels < 126 mg/dL were classified as not having diabetes.

Measures

Access to health care can be measured in terms of availability, organization, financing, utilization, and satisfaction, among other domains (16). The measures of access used in this study pertained to financing and utilization (16). Financing was measured by classifying respondents as either insured or uninsured. Respondents who answered "None" to the question "Which of the following is your primary medical coverage plan?" were classified as uninsured. Utilization was measured by 1) number of times the survey participant received health care during the past year, derived from the answer to the question "How many health care visits have you made in the past 12 months?" and 2) routine pattern of health care utilization, based on the answer to the question "What type of health care facility do you usually use?" For those on the Mexican side of the border, possible answers to the latter question included a) emergency room or urgent care clinic, b) private doctors' offices, c) public clinic (non-urgent care), d) military (i.e., the Mexican Veterans Affairs hospital (Sedena Marina), e) Mexican Social Security Institute (Instituto Mexicano de Seguro Social, IMSS), f) Mexican ministry of health (Secretaría de Salud), g) Mexican social security for state workers (Instituto de Seguridad y Servicios Sociales de los Trabajadores del Estado, ISSSTE), h) pharmacy, and i) no place. For the U.S. side of the border, possible answers included: a) emergency room or urgent care clinic, b) private doctors' office, c) public clinic, d) military (veterans affairs hospital), e) health center, f) pharmacy, and g) no place.

Results were controlled for six socio-demographic factors: age (continuous variable), sex, marital status (dichotomous variable), highest level of education attained (less than high school, high school, and high school plus some college), and occupation (white collar, blue collar, service, and not in the labor force). Covariates included BMI (continuous variable) and a dichotomized version of self-rated health ("good or above" versus "fair/poor").

Three different approaches were used to examine the relationship between access to health care and undiagnosed diabetes: 1) use of multivariate logistic regression models among all survey respondents with diabetes ("diagnosed" and "undiagnosed") to examine the association between undiagnosed diabetes and health care access indicators; 2) use of the same multivariate logistic regression models among survey respondents who self-reported not having diabetes (including those who did not have diabetes and those who had diabetes but were unaware of their condition) to examine the association between access to health care and actually having diabetes, with age, sex, marital status, education, occupation, BMI, self-rated health, and country of residence as covariates; and 3) testing for interaction between access to health care and country of residence, and, in cases where P values for interaction were significant, further examination of the percentage of survey respondents with undiagnosed diabetes, by health care access indicator and country of residence.

RESULTS

Among the survey respondents aged 1864 years old who had fasted for at least 8 hours immediately before having their plasma glucose measured (n = 3 470), the current study identified 178 individuals with undiagnosed diabetes, 326 with diagnosed diabetes, and 2 966 persons without diabetes (Table 1). The mean age for those with diagnosed diabetes was 48.5 years. For those with undiagnosed diabetes and no diabetes, the mean ages were 38.0 years and 35.5 years, respectively. There were no significant differences by sex, marital status, or occupation among the three groups ("no diabetes" "undiagnosed diabetes," "diagnosed diabetes"). There was a significant racial/ethnic difference by diabetes status, with Hispanics comprising 98.1% of those with undiagnosed diabetes but only 70.3% of the total population. Although residents of the Mexican side of the border represented only 44.2% of the total study sample, they represented 73.6% of the cases of undiagnosed diabetes. Regardless of diagnostic status, persons with diabetes had, on average, significantly lower educational attainment and were significantly more likely to be obese than persons without diabetes (P < 0.001). Those without diabetes had the best self-rated health, followed by those with undiagnosed diabetes and then those with diagnosed diabetes.

The percentage of uninsured was higher among persons with undiagnosed diabetes than among persons with diagnosed diabetes but the difference was not statistically significant. However, persons with undiagnosed diabetes were more likely than those with diagnosed diabetes to report not having made any health care visits in the past year (39.2% versus 13.4%) and not having a place to go for routine health care (16.6% versus 3.7%) (P < 0.01 for both indicators).

The multivariate logistic analyses (Tables 2, 3, and 4) examined the relationship between access to health care and undiagnosed diabetes. After adjusting for age, sex, marital status, education, occupation, BMI, self-rated health, and country of residence, it was determined that persons with undiagnosed diabetes were significantly more likely than those with diagnosed diabetes to report being uninsured (OR 2.6, 95% CI 1.06.6) and having no place to go for routine health care services (OR 4.5, 95% CI 1.414.1).

Interactions between living on the U.S. side of the border and having insurance were significant for both the diabetic population and those not reporting diabetes (P = 0.004 and 0.045, respectively) (Table 5). For the diabetic population, the interaction between living on the U.S. side of the border and number of health care visits made in the past year was also significant (P = 0.027) (Table 5). The percentage of those with undiagnosed diabetes in the U.S. border region diabetic population was significantly higher among the uninsured than among the insured (28.8%, 95% CI 11.5%46.3% versus 9.1%, 95% CI 1.5%16.7%; P < 0.05) (Table 5). Furthermore, on the U.S. side of the border, the number of health care visits made in the past year was significantly associated with undiagnosed diabetes: among those who had not made any health care visits in the past year, 40.8% (95% CI 19.6% 62.0%) were undiagnosed, whereas among those who had made 1 to 3 visits, 23.4% (95% CI 9.9%36.9%) were undiagnosed; among those who received care 4 times or more, 2.4% (95% CI 0.9%5.7%) were undiagnosed. Among survey respondents living on the U.S. side of the border who self-reported not having diabetes, the percentage of those with undiagnosed diabetes was significantly higher among the uninsured than among the insured (3.9%, 95% CI 1.0%6.8% versus 1.1%, 95% CI 0.3%1.9%; P < 0.05).

Among the survey respondents living on the Mexican side of the border, this pattern did not exist, although the percentage of undiagnosed diabetes was generally higher in each population category versus the U.S. side of the border. However, there were some variations in the percentage of undiagnosed diabetes on the Mexican side of the border by type of health care facility used. For example, the percentage undiagnosed was significantly higher among those who reported no place to receive health care versus those who reported usually using an emergency room/urgent care clinic or publicly-funded facility for routine health care services (61.2%, 95% CI 43.6%78.4% versus 62.4%, 95% CI 44.2%80.6% and 35.6%, 95% CI 23.3%47.9%, respectively) (all, P < 0.01). Among Mexican adults who reported not having diabetes, the percentage of those with undiagnosed diabetes was significantly lower among those who used private care (3.5%, 95% CI 1.0% 6.0%) and those who used publicly funded care (5.6%, 95% CI 3.4% 7.8%) versus those who usually used emergency room/urgent care for routine health care services (19.4%, 95% CI 7.6%31.2%) (all, P < 0.01).

DISCUSSION

Persons with undiagnosed diabetes are at high risk for diabetes-related complications (2, 5). Interventions that can reduce the risk of or at least delay the development of diabetes complications require timely diagnosis of the diabetes, which in turn requires access to routine health care services. Based on a representative sample of adult residents of the U.S.-Mexico border region, findings from the current study showed that lack of access to health care was significantly associated with elevated risk of having undiagnosed diabetes, and undiagnosed diabetes was associated with a lack of both health insurance and a place to receive routine health care. When analyzing the data by country of residence, the results showed that, on the U.S. side of the border, limited access to health care due to lack of either health insurance or a place to receive routine health care was significantly associated with undiagnosed diabetes. On the Mexican side of the border, however, there was no association between these variables.

Previous studies found no relationship between education or income and risk of having undiagnosed diabetes (23, 24). However, these studies did not consider the effect of access to health care (another aspect of socioeconomic status) on diagnosis of diabetes. A recent study (25) using data from the U.S. Centers for Disease Control and Prevention's Behavioral Risk Factor Surveillance System (BRFSS) (19982001) found that persons of lower socioeconomic status were at greater risk for not receiving preventive care than those at other socioeconomic levels, and those without health insurance coverage had the greatest risk of not receiving preventive care. One study that specifically examined the effect of access to health care on diabetes diagnosis (20) found an association between limited access and being undiagnosed. In line with those findings, the results of the current study suggest that, at least for those residing on the U.S. side of the border, limited access to health care due to lack of health insurance and/or lack of a place to receive routine health care has a significant effect on the detection of diabetes.

When the study analysis was repeated, stratifying the data by country of residence, the results suggested that type of health care system might account for the difference in the association between access to health care and the detection of diabetes. Among those living on the Mexican side of the border, the percentage of undiagnosed diabetes was higher in all categories (see Table 5) versus those living on the U.S. side of the border. However, there was no significant association among those living on the Mexican side of the border between access to health care and diagnosis of diabetes. In contrast, among those living on the U.S. side of the border, access to health care was associated with detection of diabetes (i.e., respondents with a place to receive routine health care had less likelihood of having undiagnosed diabetes). This pattern appeared not only among the diabetic population but also among people who reported not having diabetes. An increase in patients' willingness to seek insurance and use health care upon receipt of a diagnosis of diabetes may have driven these findings, as shown in studies on use of health care services after diagnosis of diabetes versus several years prior (2629), which found an increase in health care utilization. Similar to a previous study (20) that found that undiagnosed status could be attributed to a lack of access to health care, the current findings indicated that, at least for those on the U.S. side of the border, access to health care plays a crucial role in determining whether or not diabetes is detected.

Based on the country-stratified data, the differences in the association between access to health care and diabetes detection on the U.S. versus the Mexican side of the border may be attributable to the type of health care systems in the two countries. When survey respondents' responses about routine patterns of health care utilization were analyzed, four main categories emerged: 1) "none" (i.e., having no place to receive routine health care), 2) emergency room or urgent care, 3) publicly funded care, and 4) private care. While the categories "having no place to receive routine health care" and "use of private care" are self-explanatory and have definitions common to both sides of the border, the "emergency room/urgent care" and "publicly funded care" categories have different, country-specific criteria. For example, in the United States, the "publicly funded" category included public clinics funded by Medicare or Medicaid, Veteran Affairs facilities, and health centers operated by communities, whereas in Mexico this category included public clinics, the Veteran Affairs hospital (Sedena Marina), and health centers operated by the IMSS, the ministry of health, and the ISSSTE. According to other studies, differences in health care systems may account for variations in the association between health care access and various health outcomes (10, 14, 30).

The current study had several limitations. First, the relatively small number of persons in the sample with undiagnosed diabetes made it difficult to analyze differences by subgroup (e.g., sex or ethnicity). Second, the study's measures of health care access did not take into account availability, organization, or satisfaction. Third, diabetes status was identified by self-report as well as lab data, allowing for the possibility of recall bias.

Nevertheless, the current study's analyses clearly indicate that limited access to health careespecially among those without health insurance and/or a place to receive routine health care servicesis associated with undiagnosed diabetes. To increase the timeliness of diabetes detection and thereby prevent diabetes-related complications and their associated economic and human costs, routine health care must be made more accessible to those who currently lack access to it. While the specific characteristics of this demographic group may differ between the two sides of the U.S.-Mexico border region, there is an urgent need in both the United States and Mexico to address the health care access gap.

Acknowledgment. This study was supported by the U.S. Centers for Disease Control and Prevention (CDC). The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the CDC.

2. U.S. Centers for Disease Control and Prevention. National diabetes fact sheet: general information and national estimates on diabetes in the United States, 2007 [page on the Internet]. Atlanta, GA: U.S. Department of Health and Human Services, CDC; 2008. Available from: http://www.cdc.gov/diabetes/pubs/ pdf/ ndfs_2007.pdf. Accessed 15 October 2009. [ Links ]